Monday, April 13, 2015

In Middleburg, PA: The Other National Limestone Quarry

Less than ten miles away from the above pictured National Limestone Quarry in Middleburg, Pennsylvania,  is another National Limestone Quarry, which became well known about ten years ago after one of its more remote corners proved to be a source for  world-class wavellite specimens. Owned by the same family, the  Middleburg, PA,, National Limestone Quarry is by all appearances a similar kind of quarry, but it is low on the radar of mineral collectors. In fact, as best as we can determine, even  Mindat is unaware of its existence.

Through prior arrangements with the owner, members of the Baltimore Mineral Society and the Chesapeake Gem and Mineral Society received permission to collect at this "dark limestone" quarry in Middleburg on Saturday, April 11, 2015. We knew it had yielded  fluorite and that "cave flowers" had been found on the berms where  collecting was permitted,

We determined the fluorite to be easy to find in cubes  up to slightly more than an inch.It occurs in veins of dolomite within large boulders of dark limestone. To separate the fluorite cubes from the dolomite encasing them is problematic; likewise to separate the dolomite veins from the limestone through which they intrude. Many of the veins are no more than an inch wide. The preferred method for collecting the fluorite is  to  whack the large boulders with such veins using a large sledge hammer and trim away as much limestone as possible from the resulting particles

A higtlight of the day was an encounter with aragonite rubble  that  clearly originated in a cave that had collapsed on a surrounding wall. Unlike the clear to pale orangish brown aragonite stones present on many of the berms, some of this aragonite demonstrated  a presence of  stalactites, stalagmites, and "cave flowers,"  The seven inch stalactite at right proved to be one of the day's premier finds along with nodular stalagmic sections and some crumbly aragonite with vugs containing impressive microscopic orangish brown aragonite needles. Since nearly all caves or caverns in the region where such material exists are public places that prohibit collecting, this quarry provided a rare such opportunity, although  the picking were slim.

Other finds included magnificent dendrites, pictured at left. Also present, were colorless calcite crystals to about five millimeters  as seen at right  within vugs occurring in a very few limestone boulders. The only other material  of notable  interest to be uncovered were  mud crack rocks.

Even with permission to also collect at the nearby National Limestone Quarry in Mt. Pleasant Mills, the Middleburg locality sufficed to occupy our group for six hours. With  two hours of collecting time remaining, we headed to to the Mt. Pleasant Mills Quarry to a spot that yielded fine barrel-shaped calcite crystals.